What Compaction Is and Why It Matters

Before a road, a building slab, a car park or a pipe trench can be finished, the ground under it must be strong. Loose soil has air in it. Under load it settles, and whatever is built on top cracks or sinks. Compaction pushes the soil particles closer together and squeezes out air, so the layer becomes dense and strong.

On most sites, fill is spread in layers called lifts, and each lift is compacted before the next one is placed. A roller, also called a compactor, does this work. It rolls back and forth over each lift until the engineer’s tests show the soil is dense enough.

Why rollers are dangerous

A soil roller looks slow and harmless. It is not. It is heavy, its weight sits high, and it spends its day near the edges of fills, trenches and embankments and on slopes. When ground at an edge gives way, a roller can overturn. Investigations of roller deaths by safety bodies such as the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) in the United States show overturning as the central hazard for roller operators. Rollers also run over and crush people on foot, because they move back and forth all day and the driver watches the drum, not the people behind.